1. Field of the Invention
This invention relates to an apparatus for the operation of the working element of an excavator such as a power shovel, and particularly pertains to the construction for attachment of the apparatus to the excavator.
2. Description of the Prior Art
Generally the boom and the arm for operating the working element such as of a hydraulic excavator are fabricated by welding sheet metal pieces each in a box-like section. Such fabrication of the boom and the arm in the box-like section as mentioned above involves a very long welding line and entails a very high cost of production. Bending load and torsional load of great magnitude are exerted on the boom and the arm and stress is concentrated on their welded parts. Thus, it is necessary that the boom and the arm be designed in heavy construction strong enough to withstand the moments produced by such external forces as mentioned above.
Further, in the conventional hydraulic excavator, since the three fulcral joints with the hydraulic cylinders serving to retain and change the postures of boom, arm and bucket are formed independently of one another and the bending and torsional moments are large in the regions of approximation between the fulcrums, the efforts directed to enhancing strength inevitably entail a great increase in weight and in the number of steps involved in the fabrication of fulcral structures, proving the manufacture to be a work of much time and labor.
Further, since the aforementioned hydraulic cylinders for retaining and changing the postures of the boom, the arm, and the bucket independently of each other are generally disposed on the outer walls along the aforementioned members, the configuration of the working extension (consisting of the hydraulic cylinders, the boom, and the arm) has no neat appearance from the aesthetic point of view.
Concerning the first of the problems mentioned above, U.S. Pat. No. 4,069,637 discloses a boom fabricated in a tubular cross section which offers strong resistance to torsional load and decreases the total length of welding lines. The invention disclosed in the aforementioned U.S. patent contemplates closing the tube ends of the boom and refusing the hydraulic cylinders inertion in the boom and, in the arrangement for attachment of hydraulic cylinders, fails to contemplate designing the attachment for further lowering moments by reason of the tubular section of the boom (arm), simplifying the process of fabrication, or improving the appearance of the configuration of the working extension.